Easy-open composite containers for packaging products under pressure, particularly, refrigerated dough products and the like, constitute a significant commercial consumer product. Typically, these containers are formed of a spirally-wound paperboard or board stock bodywall layer and an interior liner layer which may be a laminate including craft paper, foil and/or polymer plys, and exterior label layer. The spirally-wound bodywall layer usually includes a butt joint formed by the adjacent edges of the bodywall layer and forming a spiral seam extending from one end of the container to the other. The exterior label layer surrounds the bodywall layer and covers or bridges the spiral seam to reinforce such seam and prevent premature opening along the spiral seam.
Commercially significant containers of this type are disclosed in commonly assigned U.S. Pat. No. 3,981,433 which is directed to a one-step easy-open container including an inner liner layer having a pleat positioned opposite the spiral butt joint. When the outer label layer is removed, the dough and liner expand outwardly together as the liner layer pleat begins to unfold and the result of pressure on the container body causes the butt joint to open. This in turn automatically allows the inner liner to expand further and automatically open by the rapidly expanding dough thereby allowing access to the dough in the interior of the container through the spirally easy-open seam of the container.
The outer label layer surrounding the spiral seam in containers of this type is an important structural component of the container because the outer label layer bridges the butt joint of the spiral seam and maintains it in closed position. Accordingly, the label layer must utilize materials which are strong enough to prevent premature opening of the container. Such structural requirements for the label layer prevent the use of more economical low strength sheet materials for construction of the label layer.
An additional problem which is present in containers of this type having easy-open spiral seams is removal of the portion of the label layer bridging such spiral seam so as to allow easy-opening thereof. Various mechanisms have been provided for removing the label layer from its bridging relationship with such easy-open spiral seam including providing a "collar cut" through the label layer and a weak adhesive between the label layer and the bodywall layer so that the label layer may be removed circumferentially around the container and totally off of the bodywall layer. This type of opening feature is shown in U.S. Pat. No. 3,241,739 which also discloses extending the liner layer through the easy-open seam and tearing such extending portion of the liner layer away as the entire label layer is removed around a collar cut to effect easy-opening.
More recently, an overlapped edge joint in the bodywall layer for the spiral seam has been proposed in commonly assigned U.S. Pat. No. 5,251,809 to provide reinforcement to the easy-open spiral seam and to allow the use of lower quality label layers. In addition, it has also been proposed in commonly assigned U.S. Pat. No. 5,076,440 to provide a folded-over portion in the label layer to extend along the butt joint of the easy-open spiral seam to reinforce such spiral seam and allow the use of generally lower quality materials in the label layer. Other devices have been proposed to assist in tearing of the label layer along the easy-open spiral seam only without removal of the entire label layer.